The present invention relates to the field of agricultural biotechnology. Disclosed herein are DNA constructs with an embryo-specific promoter, transgenic plants comprising such DNA constructs with an embryo-specific promoter, and methods of making and using such DNA constructs and transgenic plants.
In brief, a fertile corn plant contains both male and female reproductive tissues, commonly known as the tassel and the ear, respectively. The tassel tissues form the haploid pollen grains with two nuclei in each grain, which, when shed at anthesis, contact the silks of a female ear. The ear may be on the same plant as that which shed the pollen, or on a different plant. The pollen cell develops a structure known as a pollen tube, which extends down through an individual female silk to the ovule. The two male nuclei travel through this tube to reach the haploid female egg at the base of the silk. One of the male nuclei fuses with and fertilizes the female haploid egg nuclei to form the zygote, which is diploid in chromosome number and will become the embryo within the kernel. The remaining male nucleus fuses with and fertilizes a second female nucleus to form the primary endosperm nucleus, which is triploid in number and will become the endosperm of the kernel, or seed, of the corn plant. Non-fertilized ovules do not produce kernels and the unfertilized tissues eventually degenerate.
The kernel consists of a number of parts, some derived from maternal tissue and others from the fertilization process. Maternally, the kernel inherits a number of tissues, including a protective, surrounding pericarp and a pedicel. The pedicel is a short stalk-like tissue which attaches the kernel to the cob and provides nutrient transfer from maternal tissue into the kernel. The kernel contains tissues resulting from the fertilization activities, including the new embryo as well as the endosperm. The embryo is the miniature progenitor of the next generation, containing cells for root and shoot growth of a new, young corn plant. It is also one tissue in which oils and proteins are stored in the kernel. The endosperm functions more as a nutritive tissue and provides the energy in the form of stored starch, proteins and oil, needed for the germination and initial growth of the embryo.
Considering the complex regulation that occurs during embryo and kernel development in higher plants, and considering that it is commonly grain that is a primary source of nutrition for animals and humans, key tools needed to improve such a nutritional source include genetic promoters that can drive the expression of nutrition enhancing genes. Unfortunately, relatively few promoters specifically directing this aspect of physiology have been identified. Accordingly, there is a need in the art for novel promoter sequences which are involved in kernel development, and more particularly, embryo development.